Spark gap device with cold electrodes



Sept. 9, 1947. E. e. F. ARNOTT El AL SPARK GAP DEVICE WITH COLD ELECTRODES Filed Sept. 24, 1945 f MT" 5 F I I I I Ch... i v v INVENTORS E 6. ,vzawar C'. E. Dflh/LEY.

BY 1mm ATTORNEY Patented Sept. 9, 1947 STATES PATENT "OFFICE.

SPARK GAP DEVICE "WITH COLD ELECTRODES Edward G. F. Arnott, Upper Montclair, and Clarence E. Dawley, Bloomfield, N. J assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application September 24, 1945, Serial No. 618,182:

4 Claims. 1

The present invention relates to discharge devices and more particularly to what are known as. spark gaps now commonly used in connection with pulsing of electrical wave energy and constitlltesan improvement over the structure shown in our prior Patent Number 2,411,241, issued November 19, 1946, and assigned to the same assignee as the present invention.

Devices of this type are most frequently used in a modulator to generate energy pulses of high voltage and accordingly accurate alignment of the electrodes is-necessary to maintain definite breakdown voltage during the useful life of the device.

As pointedout in the above-identified application, it has been found that despite accurate alignment of the electrodes, there is a tendency for thearc discharge: to concentrate atlocalized points even withthe employment of electrodes devoid offlsharplpoints and edges, This results in the concentrated are causing sputtering of the electrodes. with attendant building-up of material on the anodeat such points and the wearing of'ahole through the cathode adjacent to the points. at which the arc concentrates on the anode; thus destroying the useful life of the device by: causing materialhvariation in its breakdown. potential.,. The reasonfor localization of the arc residesiin the fact that the potential gradientzatzthe anode surface is highest at the point where: the end of the anode begins to round ofi.

It haslong been appreciated inthe art that the elimination of edges havin sharp radii of curvation .reduces the potential gradient, and for this reasondt has been customary to provide a hemispherical end on the anode with the radius of the. hemispherical end equal to that of the anode, with the result that the potential gradient begins to increase as the surface of the anode end changes from a cylinder to a hemisphere. Such increase, however, continues for only a short distance since the space between the electrodes is increasedat the same time with the result that in efiect the potential gradient is substantially concentrated at points on the anode surface caus ing a hole to be worn into the adjacent surface of the cathode.

Accordingly, in the above-identified application th electrodeswere so constructed that the radius of curvature does not change abruptly from a cylinder to that of a hemisphere, but are provided with curved surfaces or more nearly elliptical orparabolical surfaces. Although such changeein the. radius of curvature of the anode increased the useful life of the device by more uniformly distributing the potential gradient over the surface of the. anode, it was found that the life of such devices could still further be increased by the provision of a curved surface of a similar large radius adjacent the curved surface of the anode.

It is accordingly an object of the present invention to provide a spark gap device. wherein concentration of the arc discharge, due to an increase of the potential gradient at any point on the anode surface, is eliminated.

Another object of the present invention is the provision of a spark gap device wherein the anode is given such a radius of curvature at the extremity thereof where the potential gradient would otherwise be high, and the cathode adjacent the end of the, anode and at the extremity of the cathode, is likewise given a surface of curvature that the gradient is more equally distributed over the anode surface and are concentration is eliminated.

Another object of the present invention is the provision of a spark gap device wherein the end of the anode is given a radiusof curvature such as to eliminate arc concentration and uniformly distribute the potential gradient, and the cathode is likewise given a surface of relatively large radius of curvature to still further more uniformly distribute the potential gradient over the surface of the anode.

Still further objects of the present invention will become obvious to those skilled in the art by reference to the accompanying drawing wherein Figure 1 is a sectional view of a spark gap device constructed in accordance with the present invention.

Figure 2 is a sectional view taken on the line 11-11 of Fig, 1; and

Figure 3 is a view similar to Fig. 1 with a slight modification which the present invention may take.

Referring now to the drawing in detail, the device as shown in Fig. 1 comprises a vitreous envelope 5 closed at each end by cup-shaped members 6 and 1 formed of a metal having substantially the same coeliicient of expansion as that of the vitreous envelope, such as that commercially known as Kovar, which forms an hermetic seal with the vitreous envelope 5.

As shown in the drawings, the electrodes are supported by the end closures 6 and l and are assembled thereon prior to sealing the closures to the vitreous envelope, with the latter being accomplished so as to accuratelytand precisely align the electrodes, such as in the manner shown and described in the copending application of Ward W. Watrous, Serial No. 521,807, filed February 10, 1944, and assigned to the same assignee as the present invention.

For example, the anode 8, which may be formed from an iron or carbon-steel rod, is welded to an annular flange portion 9, the latter of which forms a suitable terminal for the device. The cathode In constituting a cylinder of metal, such as aluminum or the like, is somewhat similarly secured to the Kovar closure member 1. As will be noted, the end of the cathode is welded or otherwise afiixed about its periphery to an annular portion H, and an annular member l2 fits within the annular portion II to thus form an end wall for the cylindrical cathode ID, with such annular member 12 being provided with an exhaust tip l3, which is welded or otherwise closed after evacuation of the device and filling thereof with the desired ionizable medium, such for example, as a mixture of about 80% hydrogen and 20% argon at about 680 mm. pressure.

It will be noted that the inner end Hi of the anode 8 is elliptically rounded instead of hemispherically. It has been found, as hereinbefore mentioned, that in instances where the radius of a hemispherical end is equal to that of the anode 8, an edge results at the point where the anode end begins to round off. Tests have shown that after a comparatively few hours of life, the high potential gradient at this point on the anode surfaces causes a concentration of the arc with attendant sputtering and a build-up of material on the anode which wears a hole in the adjacent surface of the cathode.

By shaping the anode in such a manner as to eliminate edges on the surface thereof, the potential gradient is more or less uniformly distributed over the entire surface eliminating any concentration of the arc. For example, with an anode of /4" diameter, by giving the extreme end of the anode 8 a rounded contour having a radius of about 5% of an inch joining with the periphery of the /4" diameter anode by a curvature having a 1" radius, an end is provided having no sharp edge or abrupt change in the radius of curvature, which may be termed .parabolical or elliptical, where the potential gradient would otherwise increase to a high value with attendant concentration of the arc.

In addition to providing parabolical or elliptical end M, the cylindrical cathode iii is likewise provided with a curved surface I5 having a large radius of curvature and disposed adjacent the curved end it of the anode. This curved surface I5 on the cathode is provided by gradually increasing the inner diameter of the anode with its the cylindrical cathode iii adjacent the elliptical end 14 of the anode 8. In a similar manner the innermost end of the cathode is likewise gradually increased in diameter to provide a surface having a relatively large radius of curvature l6 similar to the surface I5, This increase in the inner diameter of the cylindrical cathode at the points l5 and it reduces the gradient at the end of the anode and adjacent the end of the oathode and reduces the rate at which material will be disposed on the anode due to sputtering of the cathode and at the same time more uniformly distributes the potential gradient over the surface of the anode, thus eliminating the possibility of a concentrated arc building-up material on the anode and the wearing of a hole in the cylindrical cathode.

In addition it has been found effective to groove the anode over a portion of its surface, such as shown at H in Fig. 1, or for an appreciable length extending from the inner end thereof as shown at l8 in Fig. 3. By so grooving the anode, this enables sputtered material to accumulate on the anode within the grooves without materially affecting the concentrically disposed anode 8 and cathode I, which would otherwise affect the breakdown potential of the device.

It should thus become obvious to those skilled in the art that a spark gap device operable at relatively high potentials and particularly applicable to pulsing of electrical wave energy is herein provided which is of rigid yet precise construction. Moreover, such device has a long useful life since the electrodes are provided with adjacent surfaces of such contour that the potential gradient is distributed substantially uniformly over the entire surface of the anode, thus eliminating arc concentration which otherwise causes building-up of material at points on the anode surface with puncturing of the surface of the cathode adjacent such points and destruction of the device. Also the provision of grooved surfaces on the anode enables sputtered material to be accumulated on the anode without materially affecting the spacing between the concentrically disposed electrodes, thus maintaining the breakdown potential substantially uniform over the entire useful life of the device.

Although several embodiments of the device have been herein shown and described, it is to be understood that other modifications thereof may be made without departing from the spirit and scope of the appended claims.

We claim:

1. A spark gap device comprising an envelope, an anode and a cathode rigidly supported in said envelope and concentrically and telescopically disposed relative to each other, said anode being provided with an end devoid of sharp edges or abrupt change in radius of curvature at its inner extremity and said cathode having a similar surface of curvature at its innermost extremity and also having a similar surface of curvature adjacent the inner extremity of said concentrically disposed anode but diverging with respect to the curvature of said anode to prevent concentration of the arc discharge due to a high potential gradient at any point on the anode surface.

2. A spark gap device comprising a vitreous sleeve, oppositely disposed end caps hermetically sealed to said sleeve, a hollow cylindrical cathode rigidly secured to one of said end caps and a rodlike anode projecting coaxially into said cathode and provided with an end devoid of sharp edges or abrupt change in radius of curvature at its inner extremity, and said cathode having a similar surface of curvature at its innermost extremity and also having a similar surface of curvature adjacent the inner extremity of said coaxially disposed anode but diverging with respect to the curvature of said anode to prevent concentration of the arc discharge due to a high potential gradient at any point on the anode surface.

3. A spark gap device comprising a vitreous sleeve, oppositely disposed end caps hermetically sealed to said sleeve, a hollow cylindrical cathode rigidly secured to one of said end caps, a rodlike anode projecting coaxially into said cathode and provided with an end devoid of sharp edges or abrupt change in radius of curvature at its inner extremity and said cylindrical cathode having a surface of curvature devoid of an abrupt ing their peripheral edge hermetically imbedded 10 in the respective peripheral edges of said sleeve, a rod-like anode having a grooved surface for a portion of its length and projecting coaxially of said device and provided with an end devoid of sharp or abrupt change in radius of curvature at its inner extremity and a hollow cylindrical cathode rigidly secured to one of said end caps and coaxially disposed relative to said anode and provided with a surface devoid of sharp edges of abrupt change in radius of curvature adjacent the inner extremity of said anode and having a similar surface of curvature at its inner extrem- 5 ity.

EDWARD G. F. ARNOTI'. CLARENCE E. DAWLEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 15 2,411,241 Arnott et a1 Nov. 19, 1946 2,397,982 Salzberg Apr. 9, 1946 1,655,966 Lorenz Jan. 10, 1928 1,787,699 Morrison Jan. 6, 1931 

